Strain sensing using interface waves in clad rod acoustic waveguides

Abstract

The measurement of strain in materials using clad rod acoustic waveguides has been considered recently by several authors [R. T. Harrold and Z. N. Sanjana, Proc. Soc. Plastics Eng. Conf., Washington, DC (May 1985)]. In such waveguides, axisymmetric torsional, axisymmetric radial-longitudinal, and core-guided shear modes typically propagate if the velocity of plane shear waves in the clad exceeds that velocity the core. If instead the materials are reversed, these modes are not supported but an interface wave may propagate on the core-clad boundary. In principle, such waves may propagate without attenuation if the core and clad materials properties are suitably related. The theoretical sensitivity of the attenuation and mode conversion of such nonattenuating interface waves to strain-induced variations in the geometry and elastic constants of the waveguide materials are considered in this paper. Experimental measurements using strained glass-on-glass clad rods which approximately satisfy the assumed boundary conditions are reported. Potential applications in the internal monitoring of materials are suggested. [Work supported by NASA and Simmonds Precision.]